Normal language comprehension requires contributions and cooperation from many parts of the brain, ranging from sensory areas that receive the initial physical input, through frontal and temporal areas associated with oft-characterized language subprocesses, to brain areas involved in perspective-taking and social cognition; thus a network of brain areas, in both hemispheres, is recruited during everyday language and discourse processes. Evidence for a role of the right hemisphere in normal language comprehension has accumulated over the last several decades, and researchers have proposed that each hemisphere is disposed to serve different language functions necessary for comprehension. The proposed research critically extends this work, examining the idea that some typically-studied language processes are composed of distinct contributions from each hemisphere and that other processes require input from both hemispheres in order to be engaged. Using event-related potentials and a new imaging technique known as the event-related optical signal (which provides both temporal and spatial precision), these studies will explore individual and joint contributions of the two hemispheres as they unfold and interact over time during the semantic processing of normal, plausible sentences. Because the two hemispheres communicate through the corpus callosum, individual differences in callosal size will be linked to functional asymmetries to better characterize hemispheric interaction over time. PUBLIC HEALTH RELEVANCE: Understanding how the hemispheres cooperate during language comprehension has broad implications, as many language disorders have been associated with abnormal laterally patterns or deficient hemispheric communication. Providing a fuller picture of how the two hemispheres work together thus has the potential to inform treatment options or interventions for acquired or congenital language disorders. [unreadable] [unreadable] [unreadable]